Abstract
Primary open-angle glaucoma is the second leading cause of blindness in the United States and is commonly associated with elevated intraocular pressure (IOP) resulting from diminished aqueous humor (AH) drainage through the trabecular pathway. Developing effective therapies for increased IOP in glaucoma patients requires identification and characterization of molecular mechanisms that regulate IOP and AH outflow. This study describes the identification and role of autotaxin (ATX), a secretory protein and a major source for extracellular lysophosphatidic acid (LPA), in regulation of IOP in a rabbit model. Quantitative proteomics analysis identified ATX as an abundant protein in both human AH derived from non-glaucoma subjects and in AH from different animal species. The lysophospholipase D (LysoPLD) activity of ATX was found to be significantly elevated (by ∼1.8 fold; n = 20) in AH derived from human primary open angle glaucoma patients as compared to AH derived from age-matched cataract control patients. Immunoblotting analysis of conditioned media derived from primary cultures of human trabecular meshwork (HTM) cells has confirmed secretion of ATX and the ability of cyclic mechanical stretch of TM cells to increase the levels of secreted ATX. Topical application of a small molecular chemical inhibitor of ATX (S32826), which inhibited AH LysoPLD activity in vitro (by >90%), led to a dose-dependent and significant decrease of IOP in Dutch-Belted rabbits. Single intracameral injection of S32826 (∼2 µM) led to significant reduction of IOP in rabbits, with the ocular hypotensive response lasting for more than 48 hrs. Suppression of ATX expression in HTM cells using small-interfering RNA (siRNA) caused a decrease in actin stress fibers and myosin light chain phosphorylation. Collectively, these observations indicate that the ATX-LPA axis represents a potential therapeutic target for lowering IOP in glaucoma patients.
Highlights
Glaucoma, a leading cause of blindness characterized by optic nerve degeneration and progressive visual field loss, is commonly associated with elevated intraocular pressure (IOP) [1]
We recently performed quantitative proteomic analysis of human aqueous humor (AH) derived from cataract surgery patients with normal IOP. This initial analysis revealed that ATX [24], which is a well characterized secretory protein with lysophospholipase D (LysoPLD) activity, was one of the abundant proteins in human AH. Since this protein has been considered a major source for extracellular lysophosphatidic acid (LPA) [25,26], and LPA has in turn been demonstrated to influence AH outflow facility [15], in this study we investigated the role of ATX in IOP using a small molecular weight chemical inhibitor of this protein
ATX is an abundant protein of human aqueous humor Towards our objective to identifying extracellular factors regulating AH outflow and IOP, an LC-MS proteomic analysis was performed to identify abundant proteins of human AH, using one mg of pooled AH total protein derived from 8 individual donors who underwent cataract surgery
Summary
A leading cause of blindness characterized by optic nerve degeneration and progressive visual field loss, is commonly associated with elevated intraocular pressure (IOP) [1]. While there are several classes of ocular hypotensive drugs available for treatment of glaucoma, there remains a significant unmet medical need for novel, more efficacious and targeted therapy [5,6]. This need requires that we address the gap which currently exists in our understanding of regulation of IOP and AH outflow and identification of physiological and pathological factors that influence IOP and AH outflow in both normal and glaucoma patients. The conventional or trabecular AH outflow pathway is composed of the trabecular meshwork (TM), juxtacanalicular connective tissue (JCT) and Schlemm’s canal (SC) In humans, this pathway represents a predominant route of AH drainage [3]. The levels of some of these factors have been shown to be elevated in the AH of human glaucoma patients [2,13,19,20,21]
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